The acetal compound is the reaction product of an alditol and benzaldehyde. Alditol acetals, such as MDBS (1,3:2,4-bis(4-methylbenzylidene)sorbitol) and DMDBS (1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol) derivative compounds are known compounds which find their utility as an additive in polypropylene. Acetals of substituted and unsubstituted aldehydes are also known to be useful as nucleating agents, gelling agents, processing aids, and strength modifiers in polyolefin resins, polyester resins, deodorant, and antiperspirant compositions; hydrocarbon fuels and paints.
Acetal-alditols are typically prepared by the condensation reaction of an aromatic aldehyde with an alditol containing 6 carbon atoms like sorbitol. For MDBS and DMDBS structures, such reactions involve two moles of the aldehyde and one mole of an alditol.
Several methods for the preparation of acetal-alditols have been reported in U.S. Pat. No. 4,267,110, U.S. Pat. No. 3,721,682, U.S. Pat. No. 4,429,140; U.S. Pat. No. 4,562,265; U.S. Pat. No. 4,902,807; U.S. Pat. No. 5,023,354; U.S. Pat. No. 5,731,474 and U.S. Pat. No. 6,500,964.
The hitherto reported methods suffer from several shortcomings. Majority of the earlier known processes employ various organic solvents which necessitates high temperature for carrying out the reaction thereby increasing the cost component. Furthermore, most of the solvents are very expensive and they too render the process un-economical.
Attempts have been made in the past to overcome the above mentioned shortcomings by employing the acidic catalyst for improving the yield and the versatility (ability to employ variety of substituted aldehydes) the process.
The presently known processes for the preparation of acetals which employ acidic catalysts still suffer from several limitations. Though mineral acids serve as good catalysts for the acetalization process, they are very corrosive in nature. Furthermore, the final product resulting from such processes needs to be purified by neutralizing the residual free acid. Though the yields offered by all teachings are acceptable for the practical purposes, all the methods are not effective from the perspective of versatility, environmentally friendliness, energy efficient, reliability, cost-effective, and safe production.
Ionic systems, which are examples of viscous molten salts, have a number of interesting and useful properties, and have utility, for example, as highly polar solvents, co-solvents and catalyst in synthetic chemistry. They also have been found to be useful in applications in various fields such as electrochemistry, synthesis of chemical compounds, dyes, batteries, fuel cells, photovoltaic devices, electro-deposition processes, semi conductor cleaning, pyrolysis, gasification, in applications involving cellulose dissolution, for the electroplating of metals as described, for example in U.S. Pat. No. 6,573,405, U.S. Pat. No. 7,183,433, U.S. Pat. No. 7,196,221, U.S. Patent Appl. No. 2005/0147889, U.S. Pat. No. 6,527,977, U.S. Pat. Appl. No. 2008/0307703, U.S. Pat. Appl. No. 2006/0183654, U.S. Pat. Appl. No. 2009/0247432.
Ionic liquids exhibit very low or no vapour pressure and thus, in contrast to many conventional molecular solvents produce virtually no vapours. They are therefore advantageous from a health, safety and environmental point of view.
Ionic fluids prepared from quaternary ammonium salt as one of the ions have been reported in U.S. Pat. No. 5,892,124, U.S. Pat. No. 5,104,840, U.S. Pat. No. 6,573,405, U.S. Pat. No. 7,183,433 and U.S. Pat. No. 7,196,221.
Ionic compound taught in U.S. Pat. No. 7,183,433 is prepared by mixing a quaternary amine salt of formula R1R2R3R4N+X− with a hydrogen bond donor. For example, a viscous ionic compound is prepared by mixing 0.1 mole of choline chloride and 0.1 mole of para toluene sulfonic acid. The reaction is generally endothermic, and is usually carried out by heating.
The method taught in U.S. Pat. No. 7,183,433 suffers from several limitations. Firstly, the process taught in U.S. Pat. No. 7,183,433 needs energy and secondly it is very time consuming and tedious because of the viscous nature of the end product.
Processes for preparation of acetals and di-acetals other than MDBS and DMDBS structures using ionic liquids as catalysts and/or reaction medium have been reported. For example, CN 101440025 discloses a method for preparation of ethylidene ether or ketal which employs N-methyl glyoxaline bisulphate ionic liquid catalyst. Other patents which disclose the use of ionic liquids as catalyst for preparation of acetals other than MDBS and DMDBS structures include CN 101723852, CN 101544628 and CN 1858048.
None of the hitherto reported processes for preparation of MDBS and DMDBS have employed ionic liquids as catalysts and/or reaction medium. There exists a need for process for preparation of MDBS and DMDBS which uses ionic liquids as the catalyst and or reaction medium. There also remains a need for a process for preparation of acetals, particularly MDBS and DMDBS which does not employ any expensive solvents or mineral acids.